1. Field of the Invention
The present invention relates to a gas discharge tube; and, in particular, to a gas discharge tube for use as a light source for a spectroscope, chromatography, or the like.
2. Background Art
As techniques in such a field, those disclosed in Japanese Patent Application Laid-Open Nos. HEI 7-326324 and HEI 8-222185 have conventionally been known. In the gas discharge tubes described in these publications, a sealed envelope is constituted by a side tube made of glass and a stem made of glass. Respective stem pins securing anode and cathode sections are plugged in the stem. This sealed envelope is filled with about several Torr of deuterium gas, for example. Such a gas discharge tube is known as a deuterium lamp and is utilized as a stable UV light source.
Since the conventional gas discharge tubes are configured as mentioned above, however, there have been problems as follows.
Namely, since the above-mentioned sealed envelope is made of glass as a whole from the viewpoint of freedom in processing, the temperature at the junction between the side tube made of glass and the stem made of glass exceeds 1000xc2x0 C. when they are thermally fused to each other. For protecting the anode and cathode sections against this high temperature, it is necessary to employ a floating structure in which the anode and cathode sections are separated from the junction, whereby the sealed envelope increases its dimensions, which inevitably enlarges the gas discharge tube itself.
In order to overcome the problems mentioned above, it is an object of the present invention to provide a gas discharge tube which can achieve smaller dimensions while using a side tube made of glass.
In the process of carrying out experiments for making the discharge tube smaller, the inventors have groped for a method which does not yield a high temperature when joining the side tube and the stem to each other. As a result, it has been found that the rising temperature can be prevented due to the heat conduction to the anode and cathode sections upon joining the sealed envelope if the junction between the side tube and the stem is made of a metal. Namely, it has been found that, in this configuration, heat rises only about several tens of degrees in the anode and cathode sections upon joining, so that there are no thermal damages to the anode and cathode sections even in a structure in which the side tube is made so small that the cathode and anode sections are disposed closer to the side tube.
The present invention is achieved according to this finding. In order to overcome the above-mentioned problems, the gas discharge tube of the present invention has a sealed envelope at least a part of which transmits light, the sealed envelope is filled with a gas and is provided with anode and cathode sections disposed therein, electric discharge is generated between the anode and cathode sections, so that the light-transmitting part of the sealed envelope emits predetermined light outside. The sealed envelope is comprised of a stem for setting the anode and cathode sections within the sealed envelope by way of respective stem pins independent from each other, a first peripheral portion made of a metal firmly attached to a peripheral part of the stem, a second peripheral portion made of a metal secured to the first peripheral portion by welding, and a side tube, made of glass, surrounding the anode and cathode sections and having one end sealed with the second peripheral portion.
In the present invention, for elongating the life of the discharge tube while lowering the assembling temperature of the discharge tube, the side tube itself is formed from glass, whereas a metal is employed in the junction between the stem and the side tube. Namely, the first peripheral portion made of a metal firmly attached to the peripheral part of the stem and the second peripheral portion made of a metal sealing the side tube are utilized for joining. As a consequence, the thermal damage can be avoided even when the anode and cathode sections and the junction are positioned close to each other. Hence, the discharge tube itself can be made smaller.
Preferably, the first peripheral portion has a flange portion. In this case, a simple operation of mounting a peripheral part of the side tube onto the flange makes it easier to join the metal part of the stem and the metal part of the side tube to each other. Further, this flange portion can be utilized as a reference position with respect to the light-emitting part of the discharge tube.
Preferably, the second peripheral portion has also flange portion being secured with respective flange portion of the first peripheral portions by welding. Employing such a configuration facilitates the operation of welding metals to each other as the flanges of the stem and side tube are faced to each other, whereby the welding operation such as electric welding, laser welding, or the like can be made more reliable.
More preferably, each of these flange portions is provided with a positioning part. The position of the light-emitting part of the discharge tube can accurately be determined by use of this positioning part.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.